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Need expert opinion on PS/2 port.

Hello everyone,

I recently had a problem with my ps/2 keyboard not working. I read online that it may be the ps/2 port and that a CMOS reset (taking cmos battery out, waiting and putting battery back in) might fix the problem. Sure enough it worked like a champ and I am now typing this message using my ps/2 keyboard.

The problem has been solved, however I don't really know why it happened. For information, the problem first appeared after I switched my mobo to a new case and added a media card reader (via usb mobo header). Is this related? I honestly don't know. It would be great if an expert on how the I/O systems on mobos worked could chime in and give me an explanation. Its really bugging me. Thank you.
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  1. Did you try rebooting before removing the CMOS battery?

    I have seen many systems with PS/2 keyboards that if you unplug it while the system is on and plug it back in it wont always work, i have also seen others where if its unplugged even for a second after you hit the power button it wont work until you reboot. PS/2 is a lot more finicky than USB is and has more issues with hot plugging.
  2. hunter315 said:
    Did you try rebooting before removing the CMOS battery?

    I have seen many systems with PS/2 keyboards that if you unplug it while the system is on and plug it back in it wont always work, i have also seen others where if its unplugged even for a second after you hit the power button it wont work until you reboot. PS/2 is a lot more finicky than USB is and has more issues with hot plugging.


    I did try a a reboot, and I tried shutting down completely, plugging it back in and booting back up. I've also noticed that the media card reader is running much faster now since I cleared the CMOS. Its was very sluggish before. Very confusing.
  3. Best answer
    Clearing the CMOS probably forced the system to properly reassign IRQ's and memory mapped IO ranges.

    IRQ conflicts usually result in the symptoms you have experienced. The PS/2 keyboard port doesn't like to share an IRQ. USB is designed from the beginning to share an IRQ. If both of these IO ports/hubs were assigned the same IRQ then the PS/2 port just won't respond and the USB port will respond at less than optimal performance.
  4. ko888 said:
    Clearing the CMOS probably forced the system to properly reassign IRQ's and memory mapped IO ranges.

    IRQ conflicts usually result in the symptoms you have experienced. The PS/2 keyboard port doesn't like to share an IRQ. USB is designed from the beginning to share an IRQ. If both of these IO ports/hubs were assigned the same IRQ then the PS/2 port just won't respond and the USB port will respond at less than optimal performance.



    That makes complete sense. Thank you for answering. I thought IRQ conflicts were an old school problem. Any idea why this may have happened? Is it a fluke? Thank you.
  5. Best answer selected by wwusa83.
  6. wwusa83 said:
    That makes complete sense. Thank you for answering. I thought IRQ conflicts were an old school problem. Any idea why this may have happened? Is it a fluke? Thank you.

    Sometimes the automatic IRQ assignment doesn't work quite right. Sometimes it can be attributed to a deficiency in the BIOS code.
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